Polyimides have found wide use in the semiconductor industry as insulating or passivating materials in electronic components. This use is documented in the form of U.S. patents which disclose the use of polyimides, polyimide-polyamide or like materials, among which are: U.S. Pat. Nos. 3,700,497 Epifano et al; 3,846,166 Saiki et al; 3,486,934 Bond; 3,515,585 Chamberlin et al; 3,985,597 Zielenski; and 4,367,119 Logan et al.
High density electronic components have necessitated the development of dielectrically isolated semiconductor devices. Isolation between active and passive devices has been achieved using pockets or trenches of dielectric within structural regions of conductor and semiconductor materials. Examples of such structures are described in U.S. Pat. Nos. 3,766,438 Castrucci et al.; 3,796,613 Magdo et al.; 3,961,355 Abbas et al.; 3,985,597 Zielenski; 4,160,991 Anantha et al.; and 4,333,794 Beyer et al. Polyimides are frequently used as the dielectric material within the trenches of the semiconductor structures.
Filling of the pockets or trenches in semiconductor structures with a polyimide dielectric material is often accomplished using multiple coating processes. Each solution coating of the desired polyimide dielectric is followed by a plasma etch-back step in an attempt to planarize the surface area coated (which includes not only the trench, but also multiple geometries in the area surrounding the trench). Such multiple coating and etch-back steps are not only costly, but increase the possibility of contamination of the electronic component during processing.
The polyimide dielectric material is frequently applied to the surface of a semiconductor structure via solution coating, wherein the polyimide is dissolved in a suitable solvent, the solution is applied to the substrate, and the solvent is evaporated away, leaving a film of polyimide on the substrate surface. Often the viscosity of the solution of the desired polyimide is too high to facilitate proper application to the substrate. This problem has been solved by utilization of polymerizable oligomers which can be reacted in situ (on the substrate surface) to produce the desired polyimide dielectric. This method of producing dielectric electronic components is described in U.S. patent application Ser. Nos. 556,731 and 556,734, both filed Nov. 30, 1983 (assigned to the assignee of the present invention). The reaction of the polymerizable oligomers to produce a cured polyimide film is carried out using a thermal cure, with the temperature of cure depending on whether a catalyst is used to increase the reaction rate at lower temperatures. A statement was made in U.S. application Ser. No. 556,734 that theoretically radiation assisted cures were possible wherein radiation could be used to initiate the photosensitive catalyst, but there was no discussion of the sole use of radiation to cure the polymerizable oligomers. Application Ser. No. 556,731 lists radiation assisted cures or radiation curing as a possible method of cure, but states that thermal cure is preferred in any event due to simplicity and low expense.
It has previously been recognized that reaction of polymerizable oligomers containing vinyl or acetylinic groups may be initiated using radiation as an alternative to a thermal (oven) cure. For purposes of this discussion and the claims made herein, "radiation" should be interpreted to include both photon (ultraviolet light from 150 nm-600 nm) and radiation emission sources such as X-ray, electron beam, and ion beam. Depending on the oligomer, it may be necessary to add an additional reactant which is sensitive to the radiation in order to increase the speed and probability of oligomer reaction. Examples of such photo-initiated reactions are described in U.S. Pat. No. 4,164,458 Patel, and by Gupta et al., in "Photo Crosslinking and Photografting of Vinyl Polymers Using Poly(styrene-co-p-vinyl-benzophenone-p'-tert-butyl perbenzoate) as a Comonomer" Journal of Polymer Science: Polymer Chemistry Edition, Vol. 20, 147-157 (1982). The Patel patent provides a method wherein a mixture of diacetylene monomer, oligomer, and/or polymer is combined with a thermoplastic crosslinkable polymer, and the combination is subjected to actinic radiation or high energy ionizing radiation in order to achieve inter reaction between the various components of the mixture. Gupta et al. discuss benzophenone-triplet photochemical crosslinking of polymers, use of p-(p'vinylbenzoyl)peroxybenzoic acid-t-butyl ester photo initiator (VBPE), and a study of the photoreactivity of polystyrenes containing a low percentage of the VBPE photoinitiator. It is assumed the inventors of U.S. patent application Ser. Nos. 556,731 and 556,734 (described above) based their statements, that theoretically radiation cure or radiation assisted cure might be possible, on descriptions found within the literature, since no statement was made that radiation cure had been attempted nor that it had been successful.